The eye of the storm passed over the Batanes islands early Saturday, Philippine officials said. There were no immediate reports of damage or casualties.

China's National Meteorological Center announced a red alert, the observatory's highest, as the storm maintained its track toward Hong Kong and the Pearl River Delta. The observatory warned Usagi will impact coastal areas of Zhejiang and Fujian provinces.

The U.S. Navy's warning center predicted that Usagi will make landfall near Hong Kong with weaker but dangerous sustained winds of 180 kph (113 mph) early Monday morning.

In Taiwan, nearly 2,500 people were evacuated from flood-prone areas and remote mountainous regions. Torrential rains were reported along the eastern coast and in the south as officials warned of cumulative rainfall of 1,000 millimeters (39 inches) along the east coast.

Usagi retains a massive diameter of 1,100 kilometers (680 miles), with its outer rain bands extending across the main northern Philippine island of Luzon and all of Taiwan. Taiwan's Central Weather Bureau warned winds of 100 kph (63 mph) could hit Taipei.

In the Philippines, the Batanes Islands were under the highest storm alert, while lower warnings were raised in at least 15 northern provinces where officials warned of flash floods, landslides and storm surges.

In Hong Kong, Cathay Pacific Airways said Saturday that flights are unaffected but warned of delayed and canceled flights from Sunday evening to Monday morning. The airline urged passengers to postpone non-essential travel on those two days.